The present invention relates in general to pipe-bending machines, and in particular to a pipe-bending machine having a rotatable bending table provided with a bending form and with a clamping jaw movable toward and away from the bending form, a stationary machine stand supporting for free longitudinal displacement a feeding carriage with an adapter sleeve rotatable about its center axis and having an opening device; the bending form and the clamping jaw are provided, respectively, with two juxtaposed peripheral grooved sections of different curvatures, both the bending form and the clamping jaw being rotatably mounted on the bending table and being coupled to assigned driving means which adjust the matching curved grooves in the form and in the jaw to face each other.
A pipe-bending machine of the aforedescribed type is known from the German published patent application No. 26 26 202. In this known design, the bending form and the corresponding clamping jaw have clamping surfaces in the form of a rectilinear groove cooperating with one or more curved clamping grooves the radius of which corresponds to the radius of the processed pipe; driving means for adjusting the angular positions of the form and the clamping jaw relative to the bending table are assigned both to the jaw and to the form in such a manner that the rectilinear grooves or the curved grooves lie opposite each other. This prior-art bending machine, designed by the same inventor as in the present invention, fulfills the objective to bend in a single working cycle the pipe into several arcs without intermediate rectilinear lengths. In other words, the pipes in this prior-art machine are clamped at a single adapter sleeve, whereupon the pipe arc produced by one curved section of the bending form immediately adjoins the pipe arc produced by the other curved section of the form. Both successive pipe arcs in this solution have the same radius of bending. The solution according to the German published patent application No. 26 26 202 has proved successful in practice and in comparison with other pipe-bending machines known in the art has a significantly reduced number of component parts resulting in substantially easier operation. The disadvantage of this solution, however, is the fact that during a single clamping in the adapter sleeve different bending radii could not be attained.
In bending pipes it has been generally sought to make consecutive pipe arcs with the same radii of curvature so as to avoid the exchange of bending forms during the bending process on one pipe. There are, however, many instances when a single bending radius cannot be employed or is undesirable. For example, it is frequently desirable that in bending muffler pipes for motor vehicles a bending radius is to be used at which the muffler pipe reproduces a certain dynamic gas pressure. This particular bending radius, however, cannot be used advantageously for making the subsequent pipe arcs.
From the German published patent application No. 21 01 162, it is also known to bend pipes on a fully automatic, digitally controlled bending machine of the aforedescribed type so that several different bending radii can be made without the exchange of bending forms or without the readjustment of the clamping point in the feeding adjuster sleeve. For this purpose, there are provided on the bending table several bending forms of different diameters, the forms being coaxially superposed and arranged at different levels. In adjusting the pipe to another bending form the adapter sleeve clamping a portion of the pipe is lifted or lowered on the feeding carriage so as to align the pipe with the selected bending form. In this manner, the bending of pipes with different bending radii takes places at different levels. The disadvantage of this arrangement, however, is that the vertical adjustment of the adapter sleeve relative to the feeding carriage cannot be made with sufficient speed inasmuch as the weight of the adapter sleeve with the clamped pipe is too large. Also the apparatus expenditures are considerable.
From U.S. Pat. Nos. 3,299,681 and 3,147,792 there are known similar arrays of bending forms arranged at different levels. In changing the pipe from one bending form to another the desired bending form is brought into a corresponding vertical position by means of a spindle. It is true that in this solution the bending of the pipe occurs always at the same level, but again the lifting or lowering of the whole pack of bending forms by means of a spindle requires a relatively long time, and the machine in the range of the bending forms is too bulky.
In order to perform the bending operation always at the same vertical position relative to the bending table while achieving a fast exchange of the bending form, in the German published patent application No. 27 46 721 it has been devised that the bending forms are axially adjustable relative to each other, whereby in the starting position the outer bending form surrounds an inner bending form. In this manner, a very accurate bending of pipes into arcs of different radii is made possible, particularly on digitally controlled pipe-bending machines. Such machines have proved to be successful; nonetheless, due to the coaxial arrangement of bending forms, a certain discontinuity or difference is always present in the range of radii to be selected.
In the solution according to the above-mentioned published patent application No. 26 26 202 it is possible to bend the pipe into successive arcs of the same bending radius without intermediate straight lengths; the solution according to the German published patent application No. 27 46 721 enables the bending of pipes at different bending radii and with straight intermediate lengths between the arcs.